An automatic transmission for a vehicle automatically shifts into a shift-speed. The shift-speed is determined based on driving parameters, such as vehicle speed and throttle valve opening (called “throttle opening” hereinafter). Hereinafter, the term “automatic transmission” should be understood to include a continuously variable transmission that automatically forms shift-ratios, from a plurality of predetermined shift-ratios, that are determined to be suitable for driving parameters such as vehicle speed and throttle opening.
In order to determine whether to shift to another shift-speed, a shift-pattern, usually having parameters of vehicle speed and throttle opening, is considered to determine if driving conditions have significantly changed.
Referring to exemplary shift-patterns shown in FIG. 1, determination of whether shifting is required is explained hereinafter.
FIG. 1 shows usual 1->2 upshift and 2->1 downshift shift-patterns. Point “P1” of FIG. 1 denotes a driving state where a vehicle is running at a speed of V1 at a first shift-speed, with a throttle valve opening of TH1 by a driver's operation of an accelerator pedal. When the vehicle speed increases such that it becomes greater than a threshold vehicle speed (V0), for example, when the vehicle speed becomes that at point P2, i.e., at V2, the automatic transmission up-shifts to a second shift-speed.
Similarly, when the driver further operates the accelerator pedal such that the throttle opening becomes greater than a threshold opening (TH0), for example, when the driving state corresponds point P3, i.e., at TH3 the automatic transmission shifts down back to the first shift-speed.
Preferably, such shift-patterns should be set dependent on driving conditions such as driver's driving propensity, and/or shifting modes, such as economy and power modes. Therefore, various shift-patterns may be used. For example, shifting can be determined based on a shift-pattern corresponding to a driver-selected shifting mode such as economy or power mode. As another example, a driver's driving propensity (for example, a driving propensity index denoting how sportily the driver would like to drive) can be learned, and the learned value can affect alteration of shift-patterns.
However, according to the prior art, an automatic transmission changes its shift-pattern among only a few predetermined shift-patterns. Therefore, further enhancement in reflecting of driving conditions is required. Furthermore, learning a driver's propensity takes a lot of time, so a driver's current propensity and current driving circumstances are not immediately reflected.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.